30) C

There is no mention of women seeking advice from their own mother in the text. So, we cannot make a conclusion about this. So, A is wrong.

B states that mothers who find baby care difficult buy self-help books. We do not know which mothers buy these books. This would be wrong assumption to make and hence, B cannot be a conclusion.

C is correct because the text states that some mothers had tried to implement routines of feeding and sleeping as advised by self-help books but could not do so. Therefore, this can be a conclusion.

D is not necessarily true. The text states that one in six women who used books said that the books had made them feel like a failure. We do not know whether these books helped other women or not so we cannot say that the books are doing more harm than good.